1. Field of the Invention
The present invention relates to a fastening mechanism for an access lid of a subsurface chamber for servicing aircraft.
2. Description of the Prior Art
At modern aircraft terminals the servicing of aircraft on the ground is frequently performed using subsurface pits, which frequently are prefabricated, and which are installed at aircraft docking, fueling and loading areas beneath the surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits forming the subsurface chambers are typically constructed of fiberglass, steel, concrete or aluminum, and are usually constructed as complete enclosures with surrounding walls, a floor, at least one upright wall, and an access lid at the top of the wall which, when closed, lies substantially flush with the surface of the tarmac. The pits are installed below the surface of loading and refueling aprons at aircraft terminals, remote parking locations and aircraft maintenance bases.
The purpose of the pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to aircraft in a docking area, the provision of air for cooling an aircraft interior, the provision of pressurized air for starting aircraft engines, and other aircraft support activities on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate. The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with great efficiency at a central location and piped or cabled to terminations in the subsurface pits, as contrasted with the use of mobile generating or supply vehicles.
The subsurface pits which are located below the aircraft terminal area house valves, junction boxes, cooling air terminations and other terminal equipment used to service an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from the pits through hatches therein and coupled to the docked aircraft to supply the aircraft with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power.
The pits are constructed with hinged, disc-like hatches within a more expansive, generally, rectangular or circular lid. The hatches are ordinarily used to withdraw fueling lines and the like, and when properly counterbalanced, can be lifted using one hand. Both the hatches and lids must be constructed of heavy-duty aluminum or steel, or some other strong material, as they must be able to withstand the weight of an aircraft as the tires of an aircraft roll across the docking surface or maintenance pad surface. Larger pit lids for servicing aircraft are frequently counterbalanced in the manner described in U.S. Pat. No. 4,467,932. Counterbalancing a pit lid in this manner allows a lid that weighs many hundreds of pounds to be lifted by a person of ordinary strength using only one hand, with perhaps a force of between only ten and twenty five pounds. Therefore, unless some fastening mechanism is provided the lid is likely to come open when the hatch therewithin is raised.
Because the hatches within the lids must sometimes be lifted and rotated open while the lids themselves remain shut, it is frequently desirable to provide the lids with fastening mechanisms so that the lids will remain closed even while the access hatches therewithin are opened. Conventional lid fastening mechanisms typically employ springs to ensure a positive latching action of the fastening mechanism to releasably secure the lid relative to a frame upon which the lid is hingedly mounted and within which the lid is seated. The spring force normally holds a latch mechanism engaged with a catch. An operating mechanism, mounted in the lid or in the frame is used to overcome the spring force and is manually manipulated to move a latch from an engaged to a disengaged position. The lid can then be lifted and rotated upwardly relatlve to the pit lid frame.
Since subsurface chambers are often exposed to long durations of extreme and hostile weather conditions, conventional spring controlled fastening mechanisms tend to deteriorate with exposure to the elements and, with time, become inoperable. The inoperability of a spring controlled fastening mechanism can sometimes be a very serious problem, since the fastening mechanism is inaccessible from above when the lid is closed. When a spring controlled fastening mechanism malfunctions with the lid in a closed condition, significant time can be expended in freeing the fastening mechanism so that the lid can be raised. Moreover, since the normal, everyday functions of servicing an aircraft are usually performed through the access hatch within the lid, a malfunctioning lid fastening mechanism can go undetected for a lengthy period of time. Moreover, the malfunction is often detected only at the time of an emergency condition when speed in opening the lid to the aircraft servicing pit is vital. For example, the entire lid is frequently opened only during some emergency condition, such as when a fuel line valve breaks. At such a time it is extremely important for maintenance personnel to be able to immediate gain access to the entire pit by opening the entire lid rather than just the hatch within the lid. However, if the fastening mechanism has malfunctioned, the lid can be stuck in the closed position.